The Steadfast Dwarven Sphere is a Dwarven Automaton that can be found in Kagrumez. After completing the second stage of the resonance gem puzzle there, the door within the room containing the Steadfast Dwarven Spider will unlock and you can proceed to the next chamber. Hit the lever, the wall lowers and you will find the Steadfast Dwarven Sphere. Like the spider, it won't attack you. Talk to it and you can make it your follower. Since it is a creature rather than an NPC, it cannot carry items for you as a follower.